1. Field of the Invention
The present invention relates to a radar apparatus utilized as a vehicle radar system or the like, and more specifically relates to an abnormality detection method for detecting an abnormality of a radar apparatus, and a radar apparatus using this abnormality detection method.
This application is based on Japanese Patent Application No. Hei 11-046055, the contents of which are incorporated herein by reference.
2. Description of the Related Art
A vehicle radar apparatus has heretofore been made practicable for obstacle detection, detecting an object within a relatively short distance so that, for example, at the time of putting a vehicle into a garage, the vehicle does not collide against an obstacle such as a telegraph pole, a block wall or the like. Moreover, research for making practicable a radar apparatus, which intercepts a target object at a relatively long distance at a high speed and at high accuracy, has been recently promoted as an alarm system for preventing a rear-end collision with a vehicle driving ahead, or a collision at the time of driving a vehicle, other than prevention of a collision against the above described stationary obstacles, or as an adaptive cruise control system (ACC) at the time of so-called auto-cruise.
For example, in the U.S. Pat. No. RE 36,095 by the present applicant, is proposed a multi-beam radar apparatus which uses a high frequency beam in a millimeter-wave band as a transmit-beam. In this publication there is disclosed a radar apparatus which improves the detection accuracy by radiating spatially overlapping beams, using a plurality of transmitter-receiver devices, and changing the combination of the transmitter-receiver devices.
Moreover, in the publication EP 0840140A1 by the present applicant, is proposed a scan beam radar apparatus which uses a high radio frequency in a millimeter-wave band as a transmit-beam. In this publication there is disclosed a method of scanning the radio frequency radiated from a primary radiator by means of a rotating reflective body and converging the reflected beam by a dielectric lens to reduce a spread angle, to thereby radiate the reflective beam in the vehicle driving direction.
However, for example, with the multi-beam radar apparatus, the detection area has an intrinsic detection area defined for each combination of respective transmitter-receiver devices, and the position of a target object. That is, an azimuth angle and a distance with respect to a vehicle are calculated by synthesizing the received data observed for each combination of these transmitter-receiver devices. Therefore, if any one of the plurality of transmitter devices or receiver devices breaks down or deteriorates to impair the sensitivity, the radar apparatus must accurately measure the sensitivity and must appropriately judge the abnormality.
Moreover, for example, with the aforesaid scan beam radar apparatus, a transmitter-receiver circuit normally adopts a pair construction, hence the azimuth error as in the multi-beam radar apparatus is not likely to occur due to deterioration of the transmission circuit or the reception circuit. On the other hand however, the detection sensitivity deteriorates evenly over all directions.
Therefore, it has heretofore been necessary to regularly measure the sensitivity of the radar apparatus and confirm that there is no abnormality therein, such- as sensitivity deterioration or the like. This sensitivity measurement however, has been performed by transporting a vehicle mounted with the radar apparatus to a test environment where a reference target is installed, transmitting and receiving a beam to/from the reference target in a state that the vehicle is halted at a predetermined test position, and measuring the reception level. Hence there is a problem that much time and man-hours are required. Moreover, the sensitivity may be impaired due to some reason, and a partial breakdown may be caused in a constituent circuit during the regular check.
Therefore, there has been devised a method for predicting the sensitivity of a radar apparatus from the detection number for the target objects which are detected for a predetermined period of time, for the purpose of detecting abnormalities in a vehicle mounted condition. With this method however, there is a problem in that the abnormality judgement varies widely according to individual conditions such as vehicle travelling state and the road environment for travelling, such that when the target object is not detected within the predetermined period of time, the estimation is not possible (or erroneous judgement is caused). Hence, a radar apparatus has been desired which can measure the sensitivity and judge the abnormality during travelling, without being affected by such individual conditions.
The present invention has been completed under such a background, and it is an object of the present invention to provide a radar apparatus which detects and judges abnormality of the radar apparatus in the normally used state of a vehicle, without transporting the vehicle to a special environment, and avoids various problems, even if a sensitivity drop or a breakdown of the transmitter-receiver devices occurs.
To solve the above described problems, with the present invention, with a radar apparatus used mounted on a vehicle and having: a beam transmission device (for example, the transmission section 30 in embodiments) for radiating a beam as a transmission signal; a beam reception device (for example, the reception section 40 in the embodiments) for receiving a signal reflected from a target object which is within a radiation range of the radiated beam; and a processing unit (for example, the detection/control section 50 in the embodiments) for detecting the position of a target object from the transmission signal and the reception signal. The processing unit has a roadbed reflection analysis device (for example, the roadbed reflection analysis circuit 51b in the embodiments) for analyzing from among the reception signals, a roadbed reflection signal reflected from a roadbed, and incorporates an abnormality judging device (for example, the abnormality judging circuit 51c in the embodiments) for judging an abnormality of the beam transmission device or the beam reception device, based on the analysis results of the roadbed reflection analysis device.
With the above described construction, the processing unit has a roadbed reflection analysis device for analyzing from among the reception signals being received, a roadbed reflection signal reflected from a roadbed, and the abnormality judging device judges that the beam transmission device or the beam reception device is abnormal, when a reflection signal is not detected from the roadbed by the roadbed reflection analysis device. Hence, abnormality in the radar apparatus can be detected and judged during travelling, without transporting and setting a vehicle in a special measurement environment to measure the sensitivity, and without depending upon the road environment, such as the presence or absence of a target object normally serving as a target of the radar apparatus.
Moreover, with the radar apparatus wherein the processing unit detects the position of the target object by using the transmission signal and the reception signal and performing frequency conversion processing, the processing unit comprises a signal separation device (for example, the signal separation circuit 51a in the embodiment) for separating a low-intensity spectrum signal not higher than a previously set predetermined intensity level, from among the received spectrum signals which have been frequency-conversion processed by the processing unit. The roadbed reflection analysis device preferably analyzes the separated low-intensity spectrum signal as the roadbed reflection signal.
With such a radar apparatus, the reflection signal from the target object normally serving as a target of the radar apparatus is comprehended as a spectrum signal having a certain peak intensity. The position of the target object is calculated by analyzing the spectrum signal having a peak intensity not less than this certain intensity. On the other hand, the reflection signal from the roadbed does not have such a strong peak, and is a power spectrum peculiar to road noise which is dispersed with low intensity. Hence, by separating such a signal not higher than a certain level and analyzing the signal, the roadbed reflection signal can be extracted and analyzed, and an abnormality can be judged by comparing the signal with the roadbed reflection signal data from the power spectrum stored for example in a memory.
Furthermore, the roadbed reflection analysis device is further provided with a correlation calculation device (for example, the correlation calculation circuit 510 in the embodiments) for calculating a correlation value between the low-intensity spectrum signal at an optional one time and the other low-intensity spectrum signal at another time. The abnormality judging device preferably judges an abnormality in the beam transmission device or the beam reception device, based on the calculated correlation value.
Generally, the roadbed reflection signal becomes different depending upon the roadbed situation and the travelling state. If the radar apparatus has normal sensitivity, there exists, within a range travelling the same roadbed, a certain correlation between the roadbed reflection signal (low-intensity spectrum signal) at optional one time and the roadbed reflection signal (the same) at another time. On the other hand, if the radar apparatus does not have normal sensitivity, and has only a noise component, the correlation between the two is observed as being very low. Therefore, with the above described construction wherein the correlation value between low-intensity spectrum signals in very short intervals is calculated by the correlation calculation device, and when the correlation between them is low, this is judged to be abnormal, it can be judged if the transmission and reception sensitivity of the radar apparatus is normal or not in an optional roadbed situation, without storing and comparing a large amount of data in the memory.
Moreover, the vehicle has a vehicle speed detection device (for example, the vehicle speed detection device 58 in the embodiments) for detecting the moving speed of the vehicle, and the roadbed reflection analysis device further has a Doppler calculation device (for example, the Doppler calculation circuit 515 in the embodiments) for calculating the Doppler shift quantity of the received spectrum signal calculated from the moving speed at the one time and the Doppler shift quantity of the received spectrum signal calculated from the moving speed at the other time. Desirably the correlation calculation device calculates the correlation value based on the Doppler shift quantity at the one time and the Doppler shift quantity at the other time.
With the above described construction, the Doppler calculation device respectively detects the moving speed of a vehicle (vehicles own speed) at one time when data sampling is performed for calculating the correlation value, and the vehicles own speed at another time, and calculates the Doppler shift quantity of the received spectrum signal, caused therein due to the respective vehicle speeds at the time of sampling. The correlation calculation device calculates the correlation value based on the relative shift quantity between the two spectra, at the time of calculating the correlation. Hence, even if the vehicles own speed varies between two detection points, by correcting this, the error in the correlation value can be corrected to perform accurate judgement.
Moreover, in the case where the radar apparatus is an FM-CW radar apparatus in the millimeter-wave band, the vehicle has a vehicle speed detection device (for example, the vehicle speed detection device 58 in the embodiments) for detecting the moving speed of the vehicle, and the roadbed reflection analysis device has a Doppler calculation device (for example, the Doppler calculation circuit 515 in the embodiments) for calculating from the detected moving speed of the vehicle, the Doppler shift quantity of the received spectrum signal in a frequency rising section of the transmission signal of the FM-modulated beam and the Doppler shift quantity of the received spectrum signal in a frequency falling section of the transmission signal. Preferably the correlation calculation device calculates the correlation value of the low-intensity spectrum signals in the frequency rising section and the frequency falling section, from the low-intensity spectrum signal detected in the frequency rising section, the low-intensity spectrum signal detected in the frequency falling section, and the respective Doppler shift quantities calculated by the Doppler calculation device.
In the FM-CW radar apparatus, the frequency of the millimeter-wave band beam to be transmitted has a frequency rising section and a frequency falling section within a certain bandwidth. The reception signal reflected from a target object is detected with a time lag depending upon the distance between the radar apparatus and the target object. Therefore, in the signal obtained by mixing the transmission/reception signals, a beat signal with a frequency which is different in the frequency rising section and in the frequency falling section is detected. The beat signal however, causes a Doppler shift which is different in the frequency rising section and in the frequency falling section, depending on the moving speed of a vehicle.
With the radar apparatus having the above described construction however, the Doppler calculation device calculates the Doppler shift quantity of the received spectrum signal in the frequency rising section of the transmission signal and the Doppler shift quantity of the received spectrum signal in the frequency falling section of the transmission signal, from the vehicles own speed detected by the vehicle speed device mounted on the vehicle. The correlation calculation device calculates the correlation value based on respective Doppler shift quantities in the frequency rising section and the frequency falling section at the time of calculating the correlation value. Therefore, even if the frequency of the FM wave rises or falls between two points to be detected or the vehicles own speed changes, the correlation value can be corrected to perform accurate judgement.